This invention relates to fluid displacement apparatus, and more particularly, to fluid compressor unit of the scroll type.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 discloses a device including two scroll members each having an circular end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between both spiral curved surfaces, thereby to seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the contact along the spiral curved surfaces and, therefore, the fluid pockets change in volume. The volume of the fluid pockets increase or decreases dependent on the direction of the orbiting motion. Therefore, the scroll type apparatus is applicable to compress, expand or pump fluids.
Typically in such scroll type fluid displacement apparatus, a pair of fluid pockets, which are defined by the line contacts between the interfitted spiral elements and the axial contacts between the axial end surface of spiral element and end plate, are formed symmetrically. The manner of forming the fluid pockets and the principle of operation of scroll type compressor unit will be described with reference to FIGS. 1a-1d. These figures may be considered to be end views of a compressor wherein the end plates are removed and only spiral elements are shown.
Two spiral elements 1 and 2 are angularly offset and interfit with one another. So that, as shown in FIG. 1a, the orbiting spiral element 1 and fixed element 2 make four line contacts as shown at four points A-D. For purposes of discussion, FIG. 1a is considered the starting point of orbiting at 0.degree.. A pair of fluid pocket 3a and 3b are symmetrically defined between line contacts D-C and line contacts A-B as shown by the dotted regions. The pair of fluid pockets 3a and 3b are defined not only by the walls of spiral elements 1 and 2 but also by the end plates from which these spiral elements extend. When orbiting spiral element 1 is moved in relation to fixed spiral element 2, in such a manner that the center 0' of orbiting spiral element 1 revolves around the center 0 of fixed spiral element 2 with a radius of 0-0' and the rotation of orbiting spiral element 1 is prevented, the location of the pair of fluid pockets 3a and 3b shifts angularly and radially towards the center of the interfitted spiral elements with the volume of each fluid pocket 3a and 3b being gradually reduced, as shown in FIGS. 1a-1d. Therefore, the fluid in each fluid pocket 3a, 3b is compressed.
The pair of fluid pockets 3a and 3b connect to one another while passing the stage from FIG. 1c to FIG. 1d, and after rotation through a 360.degree. angle as shown in FIG. 1a, both pockets 3a and 3b are disposed at the center portion 5 and are completely connected to one another to form a single pocket. The volume of the connected single pocket is further reduced by further revolution of 90.degree. as shown in FIGS. 1b and 1c. During the course of rotation outer spaces which open in the state shown in FIG. 1b change, as shown in FIGS. 1c, 1d and 1a, to form new sealed off pockets in which fluid is newly enclosed as shown in FIG. 1a.
Accordingly, if circular end plates are disposed on, and sealed to, the axial faces of spiral elements 1 and 2, respectively, and if one of the end plates is provided with a discharge port 4 at the center thereof as shown in the figures, fluid is taken into the fluid pockets at the radial outer portions and is discharged from the discharge port 4 after compression.
During the formation of the pair of sealed off fluid pockets, a pressure differential might arise between the symmetrically disposed fluid pockets. This pressure differential could arise because of the particular formation and configuration of the fluid inlet portion which is formed through the end plate of fixed scroll member, for example, when the fluid inlet portion is formed at only one location in the end plate. Another cause of the pressure differential could be non-uniform sealing of both fluid pockets resulting from manufacturing inaccuracy or wear of the scroll members. When the pressure difference between the symmetrically disposed fluid pockets arises, vibration of the apparatus will be caused by the unbalance of pressure between the fluid pockets, or irregular motion of the moving parts will be caused by the unbalanced pressure acting on the scroll members.